For WLM 8.5, I’d suggest terminating the process (right-click on its icon in the taskbar/the little box containing some other taskbar icons, right-click on it, and click on the “Exit” menu strip), then relaunching the program and logging back in to see if messaging works.

If that hasn’t work, though, then try rebooting your computer, relaunch WLM 8.5 (if necessary), log back in, and try talking to someone to see if messaging works in that case.